1. Field of the Invention
The present invention relates generally to a monitoring apparatus for a control system provided with a microcomputer and more specifically to a monitoring apparatus which can detect trouble within a microcomputer provided for a control system and can output a trouble detection command signal in case of trouble.
2. Description of the Prior Art
Recently, microcomputers have been widely used in various fields for controlling various operations. The microcomputer encapsulated within a chip (so-called microprocessor) is usually provided with a microprocessing unit (MPU) for executing various calculations or operations in accordance with control programs (software), a random-access memory (RAM) for temporarily storing various data, a read-only memory (ROM) for storing control programs, and input/output ports.
However, since trouble sometimes occurs in even a microcomputer, it is very important to monitor the operation of the microcomputer at all times and to inform the user of abnormal operations in case of trouble.
In particular, in the case of a microcomputer used for controlling a brake system an automotive vehicle, for instance, since malfunction or misoperation of the brake system caused by microcomputer trouble may readily result in a seriously-dangerous situation, it is indispensable to provide an appropriate monitoring system for a vehicle control system provided with a microcomputer.
Microcomputer troubles can be divided into roughly two groups, that is, software trouble and hardware trouble. Causes of software trouble include, for example, destruction of input data due to mixture of external noise and consequent temporary stoppage of program execution or temporary formation of an abnormal program loop without executing normal program control. On the other hand, the causes of hardware trouble, include, for example, stoppage of a clock pulse oscillator with the result that all the operations of the microcomputer stop completely.
A microcomputer monitoring method is known including the steps of: (1) outputting a program run pulse signal with a predetermined period (hereinafter referred to simply as a PR signal) from a microcomputer whenever program control is executed normally; (2) applying this PR signal to a timer circuit for monitoring the period of the PR signal; and (3) outputting a reset signal from the timer circuit to the microcomputer when the period of the PR signal exceeds a predetermined time interval thereby indicating abnormal program control, in order to compulsorily restart the program control again beginning from the start step. In this method the PR signal is periodically inverted in response to a command signal outputted in accordance with a monitoring program incorporated at the end step of the control program.
In the above-mentioned monitoring method, temporary microcomputer trouble due to, for instance, mixture of external noise can be corrected reliably. However, in a case where computer trouble due to, for instance, defective hardware occurs, even if the microcomputer is reset repeatedly, the microcomputer will not operate normally.
As already described hereinabove, in the case where a microcomputer is provided for a control system which may result in a dangerous situation in case of trouble, it is quite important to inform the user of the microcomputer trouble and further to implement fail-safe operation or to disable to control system where necessary.
A more detailed description of the prior-art monitoring apparatus for a control system provided with a microcomputer will be made with reference to the attached drawings under DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.